What if there was a shot that you could get in a doctor’s office to negate the pleasurable effects of smoking a cigarette? It would last six months or a year, and then you might need a booster shot to prevent a relapse. Would you get it or recommend it to a family member or colleague who smokes? Would you give it to a teenage son or daughter who started hanging around with friends who smoke?

Those are questions that waft to the top of your mind when you tour Selecta Biosciences, a Watertown company that said last week it had begun the first clinical trial of a product it calls SEL-068: a nicotine vaccine. In the same way a flu vaccine revs up your body’s immune system to round up flu viruses, Selecta’s vaccine would train your immune system to capture nicotine molecules in the bloodstream, barring them from entering your brain. Smoking a cigarette would have none of the calming, appetite-reducing, or focus-sharpening effects that smokers seek.

In the United States, about 46 million people smoke, according to the Centers for Disease Control and Prevention. “About half of those people try to stop in a given year,’’ says John Hughes, a psychiatry professor at the University of Vermont who studies smoking. “But only about 5 percent are able to quit forever.’’ (Hughes has been a consultant to Selecta and other companies developing antismoking products.)

BILL GREENE/GLOBE STAFF

Lab workers like Alyssa Rague are working on a nanoparticle that functions like a virus to build antibodies.

Selecta, founded in 2008 by researchers at MIT and Harvard Medical School, thinks a successful vaccine could have “a huge impact’’ on the health care system, says chief executive Werner Cautreels. “Smoking is clearly the most preventable cause of disease, and it’s one of the big contributors to health care costs going up,’’ Cautreels says. “As a result, most insurers will completely reimburse products that help people stop smoking.’’

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Selecta has raised nearly $80 million from venture capital firms, federal agencies like the National Institute on Drug Abuse, and Rusnano, an arm of the Russian government that promotes nanotechnology.

SEL-068 is very different from the flu vaccine, a cocktail of weakened flu viruses cultivated inside chicken embryos. Selecta’s product consists of synthetic nanoparticles engineered in a lab that will masquerade as viruses. (How small is nano? Flu viruses and Selecta’s particles are about 100 nanometers wide. A human hair is about 100,000 nanometers wide.) Selecta hopes the immune system will respond to its particles by learning to make antibodies that capture nicotine in the bloodstream, and keep it from getting to the brain.

To figure out the best way to produce nanoparticles, Selecta’s scientists employ tools as complex as zeta potential analyzers, which use lasers to measure the size of particles, and as simple as dishes of ice cubes. Lloyd Johnston, a senior vice president, points to a homogenizer - a metallic vessel not much bigger than a martini shaker - and notes that it could produce 10,000 doses of Selecta’s nicotine vaccine in less than a day.

Last Monday, Selecta announced the first clinical trial for SEL-068, testing it in healthy smokers and nonsmokers. “Safety is the main thing we’re looking at,’’ Johnston says, “but we’ll also be able to see the antibody levels.’’ For the vaccine to be effective, it must stimulate production of enough antibodies to soak up most of the nicotine. Future trials would examine whether the vaccine helps smokers stop smoking over the course of six months or a year.

Selecta isn’t the first company to try to develop a vaccine to help smokers quit. A Maryland company, Nabi Biopharmaceuticals, which was collaborating with GlaxoSmithKline on a nicotine vaccine, said earlier this month that it was exploring “strategic options’’ like a sale or merger. Nabi’s vaccine couldn’t prove that it was any better than a placebo in clinical trials. A Novartis vaccine met the same fate in a 2009 clinical trial.

How big could the market be for Selecta’s vaccine? Pfizer sold $755 million worth of the smoking cessation drug Chantix last year. And that drug comes with a warning that it could increase the risk of depression or suicide. Pfizer says Chantix can help 44 percent of those who take it daily to quit within 12 weeks, but other studies have found the quit rate is lower over longer periods.

Proving that SEL-068 can help smokers is the biggest hurdle for Selecta. The next one would be getting smokers to try it, likely with marketing help from a bigger pharmaceutical company.

One advantage of a vaccine, says Hughes, the UVM professor, is “you don’t have to take a pill or put on a patch every day.’’ But a drawback is the body’s immune response to nicotine may not rev up to full power for several days or weeks. “Most people, when they want to quit smoking, they want to do it today,’’ he says. “It’s impulsive.’’

And neutralizing the effects of nicotine is one thing, while addressing the reasons people reach for a cigarette is another, says Robert Sokolove, a psychiatry professor at Boston University. A drug or vaccine may help some people stop, Sokolove says, “but when there’s a stressful situation in their life, they go back to smoking, because it’s the one thing they know that takes away their stress.’’

Selecta chief executive Cautreels also raises a scenario sure to spark debate: might his company’s vaccine one day be used before someone had picked up their first cigarette, if a family had a genetic predisposition to nicotine addiction, or if a teen was simply running with the wrong crowd?

When I interviewed Cautreels, he spoke to me on his mobile phone from a bar in Moscow, where Selecta is setting up a satellite research facility. He was surrounded by smokers and drinkers. I asked whether Selecta might one day develop a vaccine for alcoholism. “Unfortunately,’’ he said, “alcohol is too small of a molecule for the antibodies to recognize, and there’s a lot of it.’’

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